Process for dehydrating cellulosic textile material

ABSTRACT

Flexible carbonaceous textile materials are produced by treating a cellulosic textile material with phosphoric acid, heating the acid-treated material at a temperature between 100* C. and 350* C. in an ammonia-containing atmosphere to produce a nonflammable, non-fusible, strong and flexible permanently dehydrated material, and carbonizing or graphitizing the product so produced to obtain the desired flexible carbonaceous textile material.

United States Patent 51 3,661,503 Didchenko et al. May 9, 1972 541 PROCESS FOR DEHYDRATING 3,304,148 2/1967 Gallagher ..23/209.1 x

CELLULOSIC TEXTILE MATERIAL 3,305,315 2/1967 Bacon 6: al. ..23/2o9.1

[72] Inventors: Rostislav Didchenko, Middleburg Heights; Lawrence Prentiss Lowell, Jr., Brookpark, both of Ohio [73] Assignees Union Carbide Corporation, New York,

[22] Filed: May 29, 1969 [211 App]. No.: 829,102

[52] U.S. Cl ..8/116 P, 23/2091, 23/2094 [51] Int. Cl ..C01b 31/07, D06m l/00 [58] Field of Search ..23/209. 1 209.2, 209.4; 8/1 16 [56] References Cited UNITED STATES PATENTS 3,179,605 4/l965 Ohsol ..252/502 Primary ExaminerEdward J. Meros Att0rneyPaul A. Rose, Robert C. Cummings and John S. Piscitello 57 ABSTRACT Flexible carbonaceous textile materials are produced by treating a cellulosic textile material with phosphoric acid, heating the acid-treated material at a temperature between 100 C. and 350 C. in an ammonia-containing atmosphere to produce a non-flammable, non-fusible, strong and flexible permanently dehydrated material, and carbonizing or graphitizing the product so produced to obtain the desired flexible carbonaceous textile material.

15 Claims, No Drawings PROCESS FOR DEHYDRATING CELLULOSIC TEXTILE MATERIAL BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to manufactured carbonaceous materials which possess textile characteristics, and more particularly, to an improved process for manufacturing the same.

2. Description of the Prior Art As disclosed in US. Patent No. 3,305,315 to R. Bacon et al., manufactured carbonaceous materials which possess all of natural carbonaceous materials attendant unique electrical, chemical, and mechanical properties are now commercially available in the form of textile materials, such as carbonaceous yarns and cloths. These materials possess the unique properties of carbonaceous materials in combination with textile properties, such as drape and hand.

Such carbonaceous textile materials are generally prepared by the thermal conversion of fibrous cellulosic textile materials. However, as pointed out by Bacon et al., one problem associated with such conversion stems from the fact that cellulosic fibers normally contain about 5 percent to 20 percent ab sorbed water which is in equilibrium with the ambient humidity. This absorbed moisture interferes with the production of flexible carbonaceous textile material in that it encourages the formation of tarry surface deposits on the individual filaments of the textile material which upon further pyrolysis decompose causing the individual filaments to stick to one another. This results in a brittle, weak product.

While it is possible to avoid this problem by thoroughly drying the cellulosic material to be treated for a long period of time and immediately thereafter carbonizing the dried material in the same oven to prevent re-adsorption of moisture, this procedure is not always possible or practical with the equipment at hand.

In order to provide a process for the production of carbonaceous textile materials from cellulosic materials wherein the carbonization may be done at any time after an initial dehydration treatment has been performed on the cellulosic starting material, Bacon et al. have proposed to permanently dehydrate the cellulosic textile starting material by a carefully controlled heat treatment to cause said starting material to undergo an approximate weight loss in the range of from about 20 percent to about 50 percent. Such heat treatment, which may be performed in an oxidizing or non-oxidizing atmosphere, commences with the initial decomposition of the cellulose molecule involving rupture of carbon-oxygen and carbon-hydrogen bonds with the evolution of water, and ends at a point just prior to the scission of the main cellulosic molecule, the rupture of carbon-carbon bonds, and the evolution of hydrogen. This results in a product which is nonflammable, non-fusible, strong and flexible, which possesses a volatile content of approximately 45 percent to 70 percent, and which possesses the characteristic physical textile attributes of the untreated cellulosic starting material.

In the preferred embodiment of the Bacon et al. process, the cellulosic textile starting material is treated with an acid solution prior to heating, and heating is conducted in an oxidizing atmosphere. According to this preferred embodiment, the starting material is first immersed in an aqueous or non-aqueous acid solution, the solvent is removed therefrom by evaporation, and the dried acid-bearing material is then heat treated in an oxidizing atmosphere at a temperature in the range from about 100 C. to 350 C. to impart a permanent dehydration to the partially decomposed material. The treated material may be conventionally carbonized at convenience and, if desired, subsequently graphitized.

As stated in the Bacon et al. patent, the use of acid moves the entire heat treating process to lower temperature levels and/or shorter heat treating time, as does the use of an oxidizing atmosphere. According to the patent, when an acid concentration of 7 percent is employed, the average time required to convert a cellulosic cloth material to a heat treated cloth material-in an oxidizing atmosphere is about 4 hours at 180 C., about 2 hours at 230 C., about 6 minutes at 250 C., and

under 2 minutes at 350 C. Rayon cloth can be converted to heat treated material after having been soaked in a 6 percent acid solution in 6 minutes in air at 235 C. However, when the heat treatment is conducted in a non-oxidizing atmosphere, significantly longer treating times are required at a given temperature.

SUMMARY OF THE INVENTION In accordance with the instant invention it has now been discovered that if the heat treatment step of the Bacon et al. patent is conducted in an ammonia atmosphere on a given cellulosic textile starting material containing a given amount of phosphoric acid it is possible to produce the strong, flexible permanently dehydrated material described in that patent at a given temperature within a period of time hitherto attainable only in an oxidizing atmosphere. The use of both phosphoric acid and ammonia is essential to produce this product within a time period equal to the time required to produce the product in an oxidizing atmosphere, and if either of these materials is not employed in the process a brittle, weak product results unless significantly longer heat treating times are employed. Any carbon or graphite fibers produced from such weak, brittle product are likewise weak and brittle. On the other hand, the heat treated material produced in accordance with this invention can be carbonized and graphitized in a conventional manner to produce a carbon or graphite fiber which is strong and flexible. Such carbon and graphite fibers have a fixed carbon content of about 15 percent more than similar products produced in an oxidizing atmosphere. Furthermore, the elimination of oxygen in the preparation of the preliminary permanently dehydrated material eliminates the possibility of combustion of the fibers if closely controlled temperature conditions are not employed.

DESCRIPTION OF THE PREFERRED EMBODIMENT The term cellulosic material as used herein and in the appended claims refers to all natural cellulosic forms (cotton, linen, jute, etc.) and all regenerated cellulosic forms such as rayon.

The phosphoric acidused may be employed in either an aqueous or non-aqueous solution. An aqueous solution has been found preferable for heat treating cellulosic yarns, and a non-aqueous solution is preferred for cellulosic textile materials such as sheets of cloth. Generally speaking, the more compacted are the individual cellulosic filaments, such as in tightly woven cloth as compared to yarns or loose woven goods, the more a non-aqueous solution is preferred.

When a non-aqueous solution is employed, such as would be the case in the conversion of starting cellulosic cloth into a heat treated carbonaceous cloth which retains the textile characteristics of the cellulosic cloth, suitable solvents include alcohols such as methanol and ethanol, and ketones such as methyl ethyl ketone.

The phosphoric acid concentration in the solution may vary from less than 1 percent to 50 percent by volume and a range of from 2 percent to 10 percent is preferred, the exact optimum depending on the particular form of textile starting material. A higher acid concentration is preferred for woven and knitted fabrics than for felts and a higher acid concentration is preferred for felts than for fibers, filaments or batting.

After the material to be carbonized is treated with the phosphoric acid solution, e.g., by soaking, it is preferably air dried, suitably at room temperature, to remove solvent and leave the acid evenly distributed on the material. After drying, the material is heat treated in an ammonia atmosphere at a temperature between C. and 350 C., preferably between 200 C. and 300 C. If desired, an inert gas or a mixture of inert gases may be present with the ammonia. However, in order to substantially reduce the time required for the heat treatment and obtain the permanently dehydrated product in a time comparable to that required to produce the product in an oxidizing atmosphere, it is necessary that the ammonia be present inan amount of at least 15 percent by volume and that the inert gas not exceed 85 percent by volume. Preferably, the ammonia is present in an amount of at least 25 percent by volume and the inert gas does not exceed 75 percent by volume.

As in the case of the Bacon et al. process, the heat treatment may vary in time from less than one minute to many hours at a temperature or schedule of temperatures not less than 100 C. or more than 350 C. The specific time and temperature depends primarily on the amount of phosphoric acid present on the textile fibers, the concentration of ammonia in the atmosphere in which heating is being conducted, and secondarily on the vehicle for the acid and the specific textile form which is being treated. Lower temperatures, of course, require longer heating times. However, under a given set of conditions, permanent dehydration of the cellulosic textilestarting material is obtained within a period of time hitherto attainable only .in an oxidizing atmosphere. Such time is significantly lower than that necessary when other nomoxidizing atmospheres are employed.

Cautionshould be exercised during the heat treatment to prevent heating in the presence of ammonia from exceeding 350 C. as the flexibility and strength of both the permanently dehydrated product and carbonized or graphitized product produced therefrom is seriously affected by heating above such temperature.

The treated material may now be conventionally carbonized at convenience and, if desired, subsequently graphitized. When this heat treated material is carbonized by a standard procedure (ASTM-D 189-61 Standard Method of Test for Conradson Carbon Residues of Petroleum Products"), it has a fixed carbon content of about 15 percent more than similar products which have been treated in an oxidizing atmosphere.

A specific example of the invention is the following:

A sample of rayon yarn (single ply, 825 denier with 720 filaments per ply) was immersed in a 6.7 percent by weight aqueous phosphoric acid solution. The treated yarn was dried by subjecting it to high velocity air at room temperature. The acid pick-up of the yarn amounted to 7.2 percent based on the dry weight of the yarn. Thereafter the dried acid-impregnated yarn was heated to 270 C. in 4 minutes in an atmosphere consisting of one-third by volume ammonia and two-thirds by volume nitrogen. The resulting yarn was flexible and strong. The thus permanently dehydrated heat treated material was subsequently carbonized by heating to 950 C. in 4 minutes under an atmosphere of nitrogen gas. The carbonized material was likewise flexible and strong. The average breaking strength of four 3 inches samples was 3.24 pounds.

When the procedure was repeated by heating to 270 C. in a nitrogen atmosphere, the filaments of the yarn tended to stick together and the product produced was weak and brittle compared to that produced in an atmosphere of ammonia and nitrogen. Upon carbonization by heating to 950 C. in 4 minutes under an atmosphere of nitrogen, a weak, brittle product was obtained. The average breaking strength of a 3 inch sample was 0.04 pound.

What is claimed is:

1. In a process for the production of a partially decomposed and permanently dehydrated material from a cellulosic textile material wherein the partially decomposed and permanently dehydrated material substantially retains the characteristic physical textile attributes of said cellulosic material which comprises first subjecting said cellulosic material to the action of an acid solution of up to 50 percent concentration and then heat treating the so-treated acid-containing cellulosic material to effect a controlled partial and selective decomposition of the cellulosic molecules of said material; the improvement which comprises employing a phosphoric acid solution as the acid solution and effecting the heat treatment in an ammonia atmosphere at a temperature in the range of from 100 C. to 350 C.

2. A process as in claim 1 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding percent by volume.

3. A process as in claim 2 wherein the inert gas is nitrogen.

4. A process as in claim 1 wherein the phosphoric acid solution has a concentration of from 1 to 50 percent.

5. A process as in claim 4 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding 85 percent by volume.

6. A process as in claim 5 wherein the inert gas is nitrogen.

7. A process as in claim 1 wherein the phosphoric acid solution is an aqueous solution and has a concentration of from 1 to 50 percent.

8. A process as in claim 7 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding 85 percent by volume.

9. A process as in claim 8 wherein the inert gas is nitrogen.

10. A process as in claim 1 wherein the phosphoric acid solution has a concentration of from 2 to 10 percent.

1 l. A process as in claim 10 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding 75 percent by volume.

12. A process as in claim 11 wherein the inert gas is nitrogen.

13. A process as in claim 1 wherein the phosphoric acid solution is an aqueous solution and has a concentration of from 2 to 10 percent.

14. A process as in claim 13 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding 75 percent by volume.

15. A process as in claim 14 wherein the inert gas is nitrogen.

i I I I 

2. A process as in claim 1 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding 85 percent by volume.
 3. A process as in claim 2 wherein the inert gas is nitrogen.
 4. A process as in claim 1 wherein the phosphoric acid solution has a concentration of from 1 to 50 percent.
 5. A process as in claim 4 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding 85 percent by volume.
 6. A process as in claim 5 wherein the inert gas is nitrogen.
 7. A process as in claim 1 wherein the phosphoric acid solution is an aqueous solution and has a concentration of from 1 to 50 percent.
 8. A process as in claim 7 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding 85 percent by volume.
 9. A process as in claim 8 wherein the inert gas is nitrogen.
 10. A process as in claim 1 wherein the phosphoric acid solution has a concentration of from 2 to 10 percent.
 11. A process as in claim 10 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding 75 percent by volume.
 12. A process as in claim 11 wherein the inert gas is nitrogen.
 13. A process as in claim 1 wherein the phosphoric acid solution is an aqueous solution and has a concentration of from 2 to 10 percent.
 14. A process as in claim 13 wherein the ammonia atmosphere contains an inert gas in an amount not exceeding 75 percent by volume.
 15. A process as in claim 14 wherein the inert gas is nitrogen. 